The present invention is concerned with the field of the manufacture of sound-absorbent materials, and has for its object a method for the manufacture of such a material.
The invention also has for object the material obtained by application of this method.
Sound-absorbent materials have for their purpose, especially in the fields of building and automobiles, the maximum absorption of sound waves travelling in the premises or dwellings.
In fact in premises or dwellings the walls of which are not lined with any sound-absorbent material, the sound waves are reflected by the said walls and inconvenience the occupants. Thus it is necessary to line the walls with such materials which more or less effectively absorb the sound waves in order to render the atmosphere of the premises or dwelling more padded and more agreeable.
In order to obtain sound-absorption at present either jute felts or sheets of natural or synthetic fibres are used, where the fibers are interlaced and possibly connected by phenol resins, or equally there are used synthetic material foams having open and communicating cells.
However the jute felts and the sheets of interlaced natural or synthetic fibres are frequently presented in the form of very fragile sheets which can be used only as lining papers or flat surfaces, their positioning further requiring qualified personnel.
Sheets of interlaced synthetic and natural fibres connected by phenol resins can be shaped by hot compression. However they are very hydrophilic and therefore cannot be used in contact with metal and a source of humidity, which is frequently the case in automobiles, especially as roof edgings and in the hood. In fact the humidity absorbed by the material stagnates and causes rusting of the metal, while diminishing the qualities of sound-absorption.
Furthermore these sheets lose a large part of their sound-absorption capacities when they are shaped by hot compression, and are heavy after the said shaping.
Synthetic cellular material foams in the form of polyurethane foam, polyvinylchloride foam of polycarbodiimide foam generally have a poor capacity for sound absorption. Moreover polycarbodiimide foam is very friable and thus difficult to utilise.